Engines of motor vehicles may use turbochargers to achieve various advantages in operation, such as increased torque, reduced fuel economy, etc. However, turbochargers may have limited operating regions.
Various approaches have been used for turbocharger boost control, and limiting of excessive turbocharger shaft speeds. One example is described in U.S. Pat. No. 6,539,714. In this example, an estimate of the turbocharger rotational speed is determined as a function of the compressor pressure ratio, the temperature signal and the engine speed signal.
The inventors have recognized several issues with such approaches, especially with regard to higher performance turbochargers that may be used that operate at higher loads and higher speeds. Further, using estimates based on prior approaches, typically generates larger estimates during transient dynamic conditions, thus resulting in a more conservative setting of turbocharger operation to reduce transient over-speed operation. In other words, due to issues of transient over-speed operation, system typically limit boost levels below that actually. For example, with regard to the example approach indicated above, transient errors may be generated because only intake conditions are considered, or because there is no dynamic compensation.
Thus, in order to address at least some of the above issues, dynamic compensation for turbocharger over-speed shaft protection may be used. In one specific example, the operation may include intake and exhaust flow dynamics, as well as turbocharger dynamics. In this way, more accurate, and dynamic, over-speed compensation may be used to more accurately limit engine and/or boost operation to limit shaft speed during dynamic turbocharger operation
As another example, an accurate estimate of turbocharger shaft speed can be determined based on a dynamic observer which uses a turbocharger torque balance as a dynamic term and a turbocharger steady state map as a static term, thereby including both the intake and exhaust side dynamics together with turbine shaft speed dynamics.